Bipolar Junction Transistor

Only available on StudyMode
  • Topic: Bipolar junction transistor, Transistor, Electronic amplifier
  • Pages : 30 (4300 words )
  • Download(s) : 88
  • Published : February 18, 2013
Open Document
Text Preview
BASIC ELECTRONICS
MODULE 3

Bipolar Junction Transistor
Prepared by

H V Balachandra Achar
Senior Lecturer,
Dept. of E&C Engg.,
M I T, Manipal

Department of Electronics and Communication Engineering,
Manipal Institute of Technology, Manipal, INDIA

Syllabus









Introduction to Bipolar Junction Transistor
BJT Operation
BJT Configurations
Tutorials
BJT Biasing
Tutorials
BJT Amplifier
Tutorials

Department of Electronics and Communication Engineering,
Manipal Institute of Technology, Manipal, INDIA

Reference Books
1. “Electronic Devices and Circuit Theory” by
Boylestad & Nashelsky,
2. “Integrated Electronics” by Millman & Halkias,

Department of Electronics and Communication Engineering,
Manipal Institute of Technology, Manipal, INDIA

Introduction
• Solid state transistor was invented by a team of scientists at Bell laboratories during 1947-48
• It brought an end to vacuum tube era
• Advantages of solid state transistor over vacuum devices: – Smaller size, light weight
– No heating elements required
– Lower power consumption and operating voltages
– Low price

Department of Electronics and Communication Engineering,
Manipal Institute of Technology, Manipal, INDIA

Introduction

Figure showing relative sizes of
transistor, IC and LED

Figure showing different transistor packages
Department of Electronics and Communication Engineering,
Manipal Institute of Technology, Manipal, INDIA

Introduction
• Bipolar Junction Transistor (BJT) is a sandwich consisting of three layers of two different types of semiconductor
• Two kinds of BJT sandwiches are: NPN and PNP

Department of Electronics and Communication Engineering,
Manipal Institute of Technology, Manipal, INDIA

Introduction
• The three layers of BJT are called Emitter, Base and Collector • Base is very thin compared to the other two layers
• Base is lightly doped. Emitter is heavily doped. Collector is moderately doped
• NPN – Emitter and Collector are made of N-type
semiconductors; Base is P-type
• PNP – Emitter and Collector are P-type, Base is N-type • Both types (NPN and PNP) are extensively used, either
separately or in the same circuit

Department of Electronics and Communication Engineering,
Manipal Institute of Technology, Manipal, INDIA

Introduction
• Transistor symbols:

Note: Arrow direction from P to N (like diode)
Department of Electronics and Communication Engineering,
Manipal Institute of Technology, Manipal, INDIA

Introduction
• BJT has two junctions – Emitter-Base (EB) Junction and Collector-Base (CB) Junction
• Analogous to two diodes connected back-to-back:
– EB diode and CB diode
• The device is called “bipolar junction transistor” because current is due to motion of two types of charge carriers – free electrons & holes

Department of Electronics and Communication Engineering,
Manipal Institute of Technology, Manipal, INDIA

Transistor Operation
• Operation of NPN transistor is discussed here; operation of PNP is similar with roles of free electrons and holes
interchanged
• For normal operation (amplifier application)
– EB junction should be forward biased
– CB junction should be reverse biased
• Depletion width at EB junction is narrow (forward biased) • Depletion width at CB junction is wide (reverse biased)

Department of Electronics and Communication Engineering,
Manipal Institute of Technology, Manipal, INDIA

Transistor Operation

Department of Electronics and Communication Engineering,
Manipal Institute of Technology, Manipal, INDIA

Transistor Operation

Un-biased transistor showing barriers at the junctions
Department of Electronics and Communication Engineering,
Manipal Institute of Technology, Manipal, INDIA

Transistor Operation

C-B junction is reverse biased – increased barrier height
Department of Electronics and Communication Engineering,
Manipal Institute of Technology, Manipal, INDIA...
tracking img